This invention relates to lithographic press dampening systems, and more particularly relates to lithographic dampening systems utilizing a brush roller.
In a lithographic press a plate cylinder has non-printing areas coated with a film of fluid from a dampening system, usually including water, and the printing areas treated with an ink from an ink form roller. The ideal dampening system rapidly establishes the proper ink-to-fluid balance so that a uniform sharp image is produced by the ink transferred to the non-water treated areas. It is therefore essential that the dampening system provide a uniform balanced distribution on the water or dampening fluid receptive areas of the plate cylinder. These dampening systems have been the major source of production difficulties in lithographic presses and for that reason many systems have been created to solve the problems of dampening, such as problems with ink roller stripping from improper ink/water balance, as well as image distortion, ink chalking and streaking.
Systems devised for providing uniform dampening include an intermittent feed dampening system in which a ductor roller oscillates between a water pan or fountain roller and a vibrator roller. This is a typical conventional dampening system. Another system for dampening includes a flap roller system in which a fountain roller having flaps intermittently contacts the vibrator roller. Other systems including brush roller systems, as well as spray systems, have been devised, but while being successful have not been entirely satisfactory. The brush roller systems provide great promise and include a system having a brush picking up fluid from a fountain and engaging a deflector bar to create a fine spray mist to transfer the fluid or water to a vibrator roller. A variety of modifications has been proposed for the brush roller system, such as a brush roller wiping a fountain roller being driven in opposite directions. Another modification has been to use a weir brush in which a leading edge of the fountain acts as a deflector bar causing a misting of the fluid on the brush. Other systems proposed include a spiral-wound brush and a spiral rib on the fountain roller deflecting a stationary brush. While these systems have effected some improvements, they have not been entirely satisfactory.